1. Field of the Invention
This invention relates to a method for the development of an image in a copying machine or printer such as an electrophotographic copying machine, an electrophotographic printer, or an electrographic recording device by using a nonmagnetic monocomponent developer. More particularly, this invention relates to a method for development that encounters no toner fracture under the impact of a Doctor blade, enjoys satisfactory drum cleanability, does not sacrifice printing properties even during continuous printing operations, and ensures ideal print quality.
2. Description of the Related Art
As an electrophotographic process, the method disclosed as in U.S. Pat. No. 2,297,691 has been widely known in the art. This method generally produces a print by imparting a uniform electrostatic charge to a photoconducting insulator (such as, for example, a sensitive drum) by means of corona discharge, projecting an optical image on the photoconducting insulator by various means thereby forming an electrostatic latent image thereon, then developing the latent image into a visible image by using a fine powder called a toner, transferring the toner image, when necessary, onto a sheet of paper, and fusing the toner image by applying pressure, heat, vapor of solvent, or light, thereby fixing the fused toner image on the paper. As the toner for developing this electrostatic latent image, the particles obtained by dispersing a coloring agent, such as a dye or carbon black in a binder resin formed of a natural or synthetic polymer resin, and pulverizing the resultant dispersed mixture to a particle size on the order of 1 to 30 .mu.m, have been used to date. These particles are called pulverized toner.
The toner of this sort is generally used either by itself or in combination with a carrier such as glass beads for the development of the electrostatic latent image.
When the toner is used in its simple form for development (method of monocomponent development), this toner is deposited on a development roller and electrically charged by a Doctor blade. The toner is then transported to the latent image part on the photoconductor by the rotation of the development roller and development of the latent image is attained because the electrically charged toner is exclusively attached to the latent image by the force of electrical attraction.
In the conventional method of nonmagnetic monocomponent development, the amount of toner to be deposited on the development roller is regulated by means of the Doctor blade; a roller made of a metallic substance or hard rubber is used as the development roller, and a pulverized toner formed of a resin such as styrene-acryl is used as the toner.
This method involves the problem of insufficient electrical charging and inferior print quality because the toner particles are crushed under the impact of the Doctor blade in the course of continued printing, suffers from a consequent increase in the proportion of small particles content, sacrifices flowability of a consequence of the entry of finely crushed toner particles into the interstices between the toner particles of the standard particle diameter, and is susceptible to degradation of the efficiency of contact between the toner and the Doctor blade.
Further, the finely crushed toner particles exhibit poor cleanability and tend to escape contacting the cleaner blade and, with the toner's low capacity for electrical charging and the increase of the amount of untransferred toner as contributory factors, tend to accumulate on the surface of the photoconductor drum possibly to the extent of interfering with the formation of the latent image and thereby contributing to the degradation of print quality.
The occurrence of the finely crushed toner particles may be attributable to the fact that the method of nonmagnetic monocomponent development exposes the toner to immense stress "when the toner is electrically charged by contacting the metallic blade on the roller made of a metallic substance or hard rubber" and the fact that the toner particles obtained by the technique of pulverization inevitably have sharp corners and, therefore, tend to sustain fractures along such sharp corners.
In contrast, suspended polymerization toner particles shaped like true spheres defy fracture, but, they entail the problem of readily assuming the most densely packed state and sacrifice flowability, have poor charging properties, roll readily on a surface and consequently tend to escape contacting the cleaner blade of the photoconductor drum, and suffer from inferior cleanability.